Upregulation of the phosphoinositide-3 kinase (PI3K)/Akt signaling pathway is a common feature in most cancers (Yuan and Cantley (2008) Oncogene 27:5497-510). Genetic deviations in the pathway have been detected in many human cancers (Osaka et al (2004) Apoptosis 9:667-76) and act primarily to stimulate cell proliferation, migration and survival. Activation of the pathway occurs following activating point mutations or amplifications of the PIK3CA gene encoding the p110α (alpha) PI3K isoforms (Hennessy et al (2005) Nat. Rev. Drug Discov. 4:988-1004). Genetic deletion or loss of function mutations within the tumor suppressor PTEN, a phosphatase with opposing function to PI3K, also increases PI3K pathway signaling (Zhang and Yu (2010) Clin. Cancer Res. 16:4325-30. These aberrations lead to increased downstream signaling through kinases such as Akt and mTOR and increased activity of the PI3K pathway has been proposed as a hallmark of resistance to cancer treatment (Opel et al (2007) Cancer Res. 67:735-45; Razis et al (2011) Breast Cancer Res. Treat. 128:447-56).
Phosphatidylinositol 3-Kinase (PI3K) is a major signaling node for key survival and growth signals for lymphomas and is opposed by the activity of the phosphatase PTEN. The phosphoinositide 3-dependent kinase (PI3K) signaling pathway is the most dysregulated pathway in hormone receptor positive breast cancer (HR+BC). The PI3K pathway is also dysregulated in aggressive forms of lymphoma (Abubaker (2007) Leukemia 21:2368-2370). Eight percent of DLBCL (diffuse large B-cell lymphoma) cancers have PI3CA (phosphatidylinositol-3 kinase catalytic subunit alpha) missense mutations and 37% are PTEN negative by immunohistochemistry test.
Phosphatidylinositol is one of a number of phospholipids found in cell membranes, and which participate in intracellular signal transduction. Cell signaling via 3′-phosphorylated phosphoinositides has been implicated in a variety of cellular processes, e.g., malignant transformation, growth factor signaling, inflammation, and immunity (Rameh et al (1999) J. Biol Chem. 274:8347-8350). The enzyme responsible for generating these phosphorylated signaling products, phosphatidylinositol 3-kinase (also referred to as PI 3-kinase or PI3K), was originally identified as an activity associated with viral oncoproteins and growth factor receptor tyrosine kinases that phosphorylate phosphatidylinositol (PI) and its phosphorylated derivatives at the 3′-hydroxyl of the inositol ring (Panayotou et al (1992) Trends Cell Biol 2:358-60). Phosphoinositide 3-kinases (PI3K) are lipid kinases that phosphorylate lipids at the 3-hydroxyl residue of an inositol ring (Whitman et al (1988) Nature, 332:664). The 3-phosphorylated phospholipids (PIP3s) generated by PI3-kinases act as second messengers recruiting kinases with lipid binding domains (including plekstrin homology (PH) regions), such as Akt and PDK1, phosphoinositide-dependent kinase-1 (Vivanco et al (2002) Nature Rev. Cancer 2:489; Phillips et al (1998) Cancer 83:41).
The PI3 kinase family comprises at least 15 different enzymes sub-classified by structural homology and are divided into 3 classes based on sequence homology and the product formed by enzyme catalysis. The class I PI3 kinases are composed of 2 subunits: a 110 kd catalytic subunit and an 85 kd regulatory subunit. The regulatory subunits contain SH2 domains and bind to tyrosine residues phosphorylated by growth factor receptors with a tyrosine kinase activity or oncogene products, thereby inducing the PI3K activity of the p110 catalytic subunit which phosphorylates its lipid substrate. Class I PI3 kinases are involved in important signal transduction events downstream of cytokines, integrins, growth factors and immunoreceptors, which suggests that control of this pathway may lead to important therapeutic effects such as modulating cell proliferation and carcinogenesis. Class I PI3Ks can phosphorylate phosphatidylinositol (PI), phosphatidylinositol-4-phosphate, and phosphatidylinositol-4,5-biphosphate (PIP2) to produce phosphatidylinositol-3-phosphate (PIP), phosphatidylinositol-3,4-biphosphate, and phosphatidylinositol-3,4,5-triphosphate, respectively. Class II PI3Ks phosphorylate PI and phosphatidylinositol-4-phosphate. Class III PI3Ks can only phosphorylate PI. A key PI3-kinase isoform in cancer is the Class I PI3-kinase, p110α as indicated by recurrent oncogenic mutations in p110α (Samuels et al (2004) Science 304:554; U.S. Pat. No. 5,824,492; U.S. Pat. No. 5,846,824; U.S. Pat. No. 6,274,327). Other isoforms may be important in cancer and are also implicated in cardiovascular and immune-inflammatory disease (Workman P (2004) Biochem Soc Trans 32:393-396; Patel et al (2004) Proc. Am. Assoc. of Cancer Res. (Abstract LB-247) 95th Annual Meeting, March 27-31, Orlando, Fla., USA; Ahmadi K and Waterfield M D (2004) “Phosphoinositide 3-Kinase: Function and Mechanisms” Encyclopedia of Biological Chemistry (Lennarz W J, Lane M D eds) Elsevier/Academic Press), Oncogenic mutations of p110α (alpha) have been found at a significant frequency in colon, breast, brain, liver, ovarian, gastric, lung, and head and neck solid tumors. About 35-40% of hormone receptor positive (HR+) breast cancer tumors harbor a PIK3CA mutation. PTEN abnormalities are found in glioblastoma, melanoma, prostate, endometrial, ovarian, breast, lung, head and neck, hepatocellular, and thyroid cancers.
PI3 kinase (PI3K) is a heterodimer consisting of p85 and p110 subunits (Otsu et al (1991) Cell 65:91-104; Hiles et al (1992) Cell 70:419-29). Four distinct Class I PI3Ks have been identified, designated PI3K α (alpha), β (beta), δ (delta), and γ (gamma), each consisting of a distinct 110 kDa catalytic subunit and a regulatory subunit. Three of the catalytic subunits, i.e., p110 alpha, p110 beta and p110 delta, each interact with the same regulatory subunit, p85; whereas p110 gamma interacts with a distinct regulatory subunit, p101. The patterns of expression of each of these PI3Ks in human cells and tissues are distinct. In each of the PI3K alpha, beta, and delta subtypes, the p85 subunit acts to localize PI3 kinase to the plasma membrane by the interaction of its SH2 domain with phosphorylated tyrosine residues (present in an appropriate sequence context) in target proteins (Rameh et al (1995) Cell, 83:821-30; Volinia et al (1992) Oncogene, 7:789-93).
The PI3 kinase/Akt/PTEN pathway is an attractive target for cancer drug development since such agents would be expected to inhibit cellular proliferation, to repress signals from stromal cells that provide for survival and chemoresistance of cancer cells, to reverse the repression of apoptosis and surmount intrinsic resistance of cancer cells to cytotoxic agents. PI3K is activated through receptor tyrosine kinase signaling as well as activating mutations in the p110 catalytic subunit of PI3K, loss of the tumor suppressor PTEN, or through rare activating mutations in AKT.
Taselisib (GDC-0032, Roche RG7604, CAS Reg. No. 1282512-48-4, Genentech Inc.), named as 2-(4-(2-(1-isopropyl-3-methyl-1H-1,2,4-triazol-5-yl)-5,6-dihydrobenzo[f]imidazo[1,2-d][1,4]oxazepin-9-yl)-1H-pyrazol-1-yl)-2-methylpropanamide, has potent PI3K activity (WO 2011/036280; U.S. Pat. No. 8,242,104; U.S. Pat. No. 8,343,955) and is being studied in patients with locally advanced or metastatic solid tumors. Taselisib (GDC-0032) is a beta-isoform sparing inhibitor of the PI3K catalytic subunit, 31× more selective for the alpha subunit, compared to beta. Taselisib displays greater selectivity for mutant PI3Kα isoforms than wild-type PI3Kα (Olivero A G et al, AACR 2013. Abstract DDT02-01). Taselisib is currently being developed as a treatment for patients with estrogen receptor (ER)-positive, HER2-negative metastatic breast cancer (mBC) and non-small cell lung cancer (NSCLC). In the phase Ia study with single agent taselisib, partial responses (PRs) were observed in 6/34 enrolled patients. All 6 responses were observed in patients with PIK3CA mutant tumors (Juric D. et al. AACR 2013), indicating the need to determine PIK3CA mutation status from patients treated with taselisib.
Recent clinical data with PI3K inhibitors has implicated PI3K delta activity as a source of gastrointestinal toxicities (Akinleye et al Phosphatidylinositol 3-kinase (PI3K) inhibitors as cancer therapeutics” Journal of Hematology & Oncology 2013, 6:88-104; C. Saura et al “Phase Ib Study of the PI3K Inhibitor Taselisib (GDC-0032) in Combination with Letrozole in Patients with Hormone Receptor-Positive Advanced Breast Cancer” San Antonio Breast Cancer Symposium—Dec. 12, 2014 (PD5-2; Lopez et al “Taselisib, a selective inhibitor of PIK3CA, is highly effective on PIK3CA-mutated and HER2/neu amplified uterine serous carcinoma in vitro and in vivo” Gynecologic Oncology (2014)
Idelalisib (GS-1101, CAL-101, ZYDELIG®, Gilead Sciences Inc., CAS Reg. No. 870281-82-6, 5-fluoro-3-phenyl-2-[(1S)-1-(7H-purin-6-ylamino)propyl]-4(3H)-quinazolinone) is a selective PI3Kδ (delta) inhibitor and approved for the treatment of chronic lymphoid leukemia (CLL) (U.S. Pat. Nos. 6,800,620; 6,949,535; 8,138,195; 8,492,389; 8,637,533; 8,865,730; 8,980,901; RE44599; RE44638). Diarrhea and colitis are among the most common adverse events reported after idelalisib treatment (Brown et al “Idelalisib, an inhibitor of phosphatidylinositol 3-kinase p110d, for relapsed/refractory chronic lymphocytic leukemia” (2014) Blood 123(22):3390-3397; Zydelig® Prescribing Information 2014; Zydelig® REMS Fact Sheet). The significant GI toxicities observed after treatment with idelalisib are consistent with the hypothesis that inhibition of PI3Kδ (delta) is a source of gastrointestinal toxicities.
There is a need for additional modulators of PI3Kα that are useful for treating cancers, particularly an inhibitor of PI3Kα that is selective for mutant PI3Kα expressing tumors relative to non-mutant PI3Kα expressing cells. There is especially a need for such an agent that selectively inhibits the PI3Kα isoform relative to the PI3Kβ, PI3Kδ, and PI3Kγ isoforms, which may be expected to result in an enhanced therapeutic window.